The present invention relates to a driving state switching unit with a synchro-mechanism that employs the synchro-mechanism to perform switching of a driving state.
In part-time four-wheel-drive vehicles capable of switching of a two-wheel-drive state (2WD) and a four-wheel-drive state (4WD), in the case where 2WD is selected, a transfer is constructed such that the transmission of power to either wheel side (generally front wheels) of the front and rear wheel sides is disconnected and that only the other wheel side (generally rear wheels) is driven. At this time, on the front wheel side where the transmission of power is disconnected, power loss will become greater in the case where all parts in the front driving system (e.g., a front propeller shaft, a front differential gear, a front axle shaft, etc.) rotate, as compared with the case where only tires and wheels are rotating.
Hence, free wheel mechanisms have hitherto been employed which are constructed so as to reduce power loss during 2WD and enhance fuel consumption, by releasing the connection between the front wheels and the front axle shaft, or by disconnecting the front axle front, during 2WD.
Also, in part-time four-wheel driving vehicles, in which a center differential unit with a limited slip differential mechanism is equipped in a transfer, driving performance as a four-wheel-drive (4WD) car, as well as conventional direct 4WD which is obtained by locking the center differential unit, is assured by setting the center differential unit free so that tight corner breaking is suppressed.
As described above, in the case of the four-wheel-drive vehicle, equipped with the free wheel mechanism, and capable of selecting center diff-4WD, there is a need to lock the free wheel mechanism being set free during 2WD, in switching the transfer from 2WD to center diff-4WD.
In the case where switching to center diff-4WD in the transfer is completed prior to locking of the free wheel mechanism, however, if a starting operation is performed before the free wheel mechanism is locked, the center differential unit will go to a idling state without transmitting engine power to the front wheels. As a result, the durability of the limited slip differential mechanism will be deteriorated and also a vehicle""s driving stability will be lost.
Also, in the case where the free wheel mechanism has not been locked, there is a possibility that synchronization of the front driving system (driving system on a non-driving wheel side) will collapse in the course of a switch from 2WD to center diff-4WD. If switching is performed with the synchronization of the front driving system being in a collapsed state, there is a possibility that at the clutch parts of the synchro-mechanism, gear grind will take place and overloading be given.
Because of this, when switching the transfer from 2WD to center diff-4WD, the free wheel mechanism needs to be locked first, and switching to center diff-4WD needs to be then completed. For instance, in the technique disclosed in Japanese Patent No. 2572064, a direct 4WD state is first gone through when the transfer is switched from 2WD to center diff-4WD. And when this direct 4WD state is detected by a switch, the free wheel mechanism is locked. In this manner the above-mentioned problem is solved.
If a dedicated switch for detecting a direct 4WD state is provided as in the above-mentioned technique, however, costs will increase by that amount. In addition, if the direct 4WD state is gone through in switching the transfer from 2WD to center diff-4WD, driving performance, which would be obtained during 2WD or center diff-4WD, cannot be obtained during the direct 4WD state, and consequently, drivers will feel a sense of incompatibility.
Therefore, it is preferable that switching be performed directly from 2WD to center diff-4WD without going through the direct 4WD state. However, it becomes important to accurately judge the synchronous state of the synchro-mechanism of the transfer in order to prevent the drawbacks due to the aforementioned synchronization collapse on the non-driving wheel side. It is also important to suppress an increase in the cost by utilizing the existing equipment without providing dedicated switches, etc.
Furthermore, the importance of the judgement of the synchronization of the synchro-mechanism is not limited to the above-mentioned switching of a driving state in the transfer, but is generally common to units that employ a synchro-mechanism to perform switching of a driving state by the connection of gears. For example, the judgement of the synchronization of the synchro-mechanism becomes important even in automatic clutch systems.
The automatic clutch system abolishes a clutch pedal and automates shift switching, by adding actuators (a clutch actuator and a shift actuator) and sensors to a normal manual transmission. In this automatic clutch system, engaging and disengaging of a clutch are performed by a clutch actuator instead of driver""s clutch-pedal manipulation. If the engaging timing of the clutch is much earlier than the synchronization of the synchro-mechanism of a transmission, however, there is a possibility that gear grind or overloading will occur. Conversely, if the engaging timing is much later, the time to change the vehicle speed will become longer and therefore the driver will feel a sense of incompatibility.
Because of this, in the conventional automatic clutch system there is a need to provide a stroke sensor (or a switch) for shift position detection in order to confirm the completion of the shift switching made by the shift actuator. However, if a dedicated switch for detecting shift position is provided in this manner, however, costs will increase by that amount.
As described above, in transfers, automatic clutch systems, etc., which employ a synchro-mechanism to perform switching of a driving state by the connection of gears, an accurate judgement of the synchronous state of the synchro-mechanism has been demanded in order to prevent gear grind or delay of switching due to a difference between the switch timing, and the synchronous timing of the synchro-mechanism, and also the realization of synchronization judging means, making use of the existing equipment, which will not incur an increased cost due to equipment such as dedicated sensors, switches, etc., has been desired.
The present invention has been made in view of such problems, and it is the object of the present invention to provide a driving state switching unit with a synchro-mechanism, capable of an accurate judgement of the synchronous state of the synchro-mechanism without providing dedicated sensors, switches, etc.
To achieve the above-mentioned object, the driving state switching unit with a synchro-mechanism of the present invention comprises a first gear and a second gear coaxially disposed; a gear connecting member axially movable so that the first gear and the second gear can be connected; and a synchro-mechanism interposed between the first gear and the second gear. By moving the gear connecting member by an electric actuator, the first gear and the second gear are connected through the gear connecting member, while they are being synchronized by the synchro-mechanism. When this occurs, control means controls a supply current to the electric actuator, and judgement means judges synchronization of the synchro-mechanism, based on a change in the supply current value to the electric actuator.
With this, the judgement of the synchronization of the synchro-mechanism becomes possible without providing dedicated sensors, switches, etc., and by performing the judgement on the basis of a change in the supply current value, an accurate judgement, corresponding even to an individual difference in the sliding resistance between members and a change in running conditions, becomes possible.
Preferably, the judgement means compares the aforementioned supply current value with an average supply current value for a predetermined time, and when a difference between the aforementioned supply current value and the aforementioned average supply current value exceeds a predetermined value, the judgement means judges that the synchro-mechanism is in a synchronous state. Since the average supply current value varies in correspondence to sliding resistance, a more accurate synchronous judgement becomes possible. Note it is preferable that the sampling of supply current values for computing an average supply current value be started, after surge current has flowed immediately after driving of the electric actuator.
Furthermore, the control means preferably controls the aforementioned supply current by setting a current indicating value to the electric actuator. And until the judgement means judges that the synchro-mechanism is in a synchronous state, the control means sets the current indicating value to a first indicating value, and furthermore, if it is judged that the synchro-mechanism is in a synchronous state, the control means sets the current indicating value to a second indicating value that is smaller than the first indicating value. With this, by first setting the current indicating value to the first indicating value that is greater, an early transition to the synchronous state becomes possible. And after synchronization, by setting the current indicating value to the second indicating value that is smaller, it becomes possible to connect gears with reliability without giving rise to gear grind, etc. Note it is preferred that the magnitude of the second indicating value be set according to a ratio of gears.
In addition, the aforementioned driving state switching unit with a synchro-mechanism may be equipped in a part-time four-wheel-drive vehicle and constructed as a driving state switching unit that performs switching of a driving state between a 2-wheel-drive state and a 4-wheel-drive state. The switching unit may further comprise a switching mechanism for switching the 2-wheel-drive state and the 4-wheel-drive state by switching an engagement relationship between the aforementioned plurality of gears through the synchro-mechanism. After switching of a driving state from the 2-wheel-drive state to the 4-wheel-drive state has been started by the switching mechanism, the judgement means may judge synchronization of the synchro-mechanism, based on a change in the supply current to the electric actuator.
With this, in the operation of switching a driving state from a 2-wheel-drive state to a 4-wheel-drive state, the judgement of the synchronization of the synchro-mechanism becomes possible without providing dedicated sensors, switches, etc., and costs can be reduced. In addition, an accurate judgement, corresponding even to an individual difference in the sliding resistance between members, a secular change, and a change in running conditions such as vehicle speed, accel opening degree and the like, becomes possible by judging synchronization on the basis of a change in the supply current value.
Preferably, the driving state switching unit with a synchro-mechanism further comprises a clutch unit, interposed between wheels which become non-driving wheels during the 2-wheel-drive state and a differential mechanism on the side of the wheels, for disconnecting the transmission of driving force from the differential mechanism to the wheels during the 2-wheel-drive state, and for transmitting the driving force from the differential mechanism to the wheels during the 4-wheel-drive state; and manipulation means for manipulating the clutch unit. In the operation of switching a driving state from a 2-wheel-drive state to a 4-wheel-drive state, in the case the judgement means judges that the synchro-mechanism is in a synchronous state, the control means maintains the synchronous state of the synchro-mechanism by controlling the supply current to the electric actuator and also switches the wheels, which are in a non-driving state, to a driving state by manipulating the clutch unit with the manipulation means. Also, when switching of the wheels to the driving state by the clutch unit is completed, the control means releases the maintaining of the synchronous state of the synchro-mechanism, and controls the supply current to the electric actuator so that the switching to the 4-wheel-drive state is completed.
Thus, when switching a driving state from a 2-wheel-drive state to a 4-wheel-drive state, the occurrence of misengagement at the synchro-mechanism, which is caused by synchronization collapse on the non-driving wheel side, can be prevented, by switching the wheels, which are in a non-driving state, to a driving state by manipulation of the clutch unit and then by completing the switching to a 4-wheel-drive state by release of the maintaining of the synchronous state of the synchro-mechanism. Particularly, in the case where there is provided a center differential unit having a limited slip differential mechanism, the deterioration of the durability of the limited slip differential mechanism due to idling of the center differential unit can also be prevented.
Furthermore, a difference in rotational speed between non-driving wheels and driving wheels is detected by detection means. If the rotational speed difference detected by the detection means exceeds a predetermined value, even in the case where the judgement means judges that the synchro-mechanism is in a synchronous state, the switching of the wheels to a driving state, which is performed by the clutch unit, is inhibited by inhibition means.
With this, even in the case where the synchro-mechanism is in a synchronous state, the switching to the driving state by the clutch unit is prevented if the rotational speed difference between non-driving wheels and driving wheels exceeds a predetermined value. Therefore, misengagement of the clutch due to a rotational speed difference can be prevented.
Moreover, the above-mentioned driving state switching unit with a synchro-mechanism may be constructed as a speed change stage switching unit for switching a stage of a speed change according to driver""s shift manipulation. The switching unit may further comprise a switching mechanism for switching a stage of a speed change corresponding to a shift position selected by a driver, by switching an engagement relationship between the aforementioned plurality of gears through the synchro-mechanism. Also, the judgement means may judge synchronization of the synchro-mechanism, based on a change in the supply current to the electric actuator, after switching of the speed change stage has been started by the switching mechanism.
With this, in the operation of switching a stage of a speed change, the judgement of the synchronization of the synchro-mechanism becomes possible without providing dedicated sensors, switches, etc., and costs can be reduced. In addition, an accurate judgement, corresponding even to an individual difference in the sliding resistance between members, a secular change, and a change in running conditions such as vehicle speed, accel opening degree and the like, becomes possible by judging synchronization on the basis of a change in the supply current value.
Preferably, the control of the supply current to the aforementioned electric actuator by the control means is performed by a feedback control of setting a current indicating value to the electric actuator. And when the judgement means judges that the synchro-mechanism is in a synchronous state, the control means sets the current indicating value to a predetermined value corresponding to a speed change ratio of speed change stages in which current indicating values have been selected.
With this, it becomes possible to connect the gears of the switching mechanism at a speed corresponding to a ratio of speed change and therefore gear grind or overloading can be prevented. Note that it is preferable to set the current indicating value smaller if a ratio of speed change becomes greater.
Furthermore, preferably a clutch for connecting or disconnecting driving force, which is engaged or disengaged by the actuator, is interposed between an engine and the switching mechanism. When the aforementioned supply current becomes a constant or approximately constant value after the current indicating value has been set to a predetermined value corresponding to a speed change ratio of the speed change stages by the control means, engaging of the clutch is started by the actuator.
With this, it becomes possible to confirm the shift switching completion of the synchro-mechanism without providing dedicated sensor, switches, etc., and costs can be reduced. In addition, it becomes possible to engage the clutch at proper timing, and driver""s sense of incompatibility due to the delay of the engaging timing of the clutch from the completion of shift switching can be prevented.